A conventional reflector antenna is parabolically shaped to provide focusing of plane waves. A “Flat Parabolic Surface” (FLAPS™) is a device currently marketed by Malibu Research, Camarillo Calif. FLAPS™ is an antenna design which utilizes a geometrically flat surface having surface features which behaves electromagnetically for incident RF radiation as though it were a parabolic reflector.
The FLAPS™ generally consists of an array of dipole scatterers. The elemental dipole scatterer consists of a dipole positioned approximately ⅛ wavelength above a ground plane on top of a dielectric layer. Incident RF energy causes a standing wave to be set up between the dipole and the ground-plane. The dipole itself possesses an RF reactance which is a function of its length and thickness. This combination of standing-wave and dipole reactance causes the incident RF to be reradiated with a specific phase shift, which can be controlled by a variation of the length of the dipole. The exact value of the this phase shift is a function of the dipole length, thickness, its distance from the ground-plane, the dielectric constant of the intervening layer, and the angle of the incident RF energy. When elements are used in an array, the elements are affected by nearby elements.
The elemental scatterer performs the function of a radiating element and a phase shifter in a space fed phased array. Since dipoles of different lengths will produce a phase shift in the incident wave, arranging the distribution and the lengths of the dipoles can be used to serve to steer, focus or shape the reflected wave. An array of such elements can be designed to reradiate with a progressive series of phase shifts so that an RF beam is formed in a specific direction. Conventional reflector antenna calculations apply to determine surface tolerances, gain, sidelobes, and other electrical antenna parameters.
Although FLAPS™ provides effective signal processing for incident RF energy, the minimum obtainable geometries being mm-scale for forming FLAPS™ surfaces based on a process comprising etching from double-layer printed-circuit boards generally limits signal processing to RF wavelengths up to only about 100 GHz. Reflectarrays that process higher frequency bands (greater than 300 GHz), such as sub-millimeter, infrared and visible, would be desirable to replace more expensive and sometimes unreliable conventional polished or diffractive optics and quasi-optics. However, besides strong challenges in obtaining required feature sizes to process shorter wavelength radiation, such a device would need to overcome challenges including modeling complexities and lack of suitable modeling software, increased attenuation loss in metals, and frequency dependent dielectric properties.